The premise of Steen's book is that nearly everyone is confused about cancer prevention. The public, for whom the book is written, is the most confused, but cannot be faulted. According to Steen, the responsibility for their confusion lies with scientists and the press. Scientists make mistakes by reporting preliminary data from inadequate and mostly "workmanlike, undistinguished" (page 3) studies. The press, in turn, repeats these mistakes, adds some of its own, and so oversimplifies a complex topic that the public, in the end, receives "unconnected facts, partial truths, and outright lies" (page 3).
To this morass of disinformation, Steen brings his solution. He will sort out the risks by reviewing what the jacket cover describes as "over 2,000 primary sources and references." After presenting evidence and ranking over 200 different risks, Steen recommends to the confused public what course they can take to prevent cancer.
It is a noble task, and Steen should not be faulted for trying to accomplish it. For some long-accepted prevention messages, Steen is right on the mark. Smoking is responsible for many cancers and deserves emphasis. Unfortunately, Steen's thesis is not well supported by this example: The public is not likely confused about the dangers of smoking; it is a public health message now 30 years old. The point is that we should not criticize Steen for reciting the obvious, nor can we evaluate his book on this basis. Rather, we must evaluate it on the greater task--the selection and review of evidence, the ranking of factors, and the recommendation of strategies--keeping in mind that Steen has criticized scientists and the press for failing to carry out their responsibilities.
My first concern relates to the strategy by which Steen has selected evidence. He has chosen a tiny fraction of the studies published on topics without informing the reader of the process that he used to make those selections. Consider for example, the association between smoking and cervical cancer. From 1966 through 1995, 39 case-control studies, 5 cohort studies, 10 comprehensive reviews, 2 meta-analyses, and at least a dozen studies of biologic parameters have been published. From these 70 publications, Steen selects 2: a case-control study showing a positive effect and a clinical study showing that, in smokers, nicotine(Drug information on nicotine)--a marker of exposure--reaches the cervical epithelium. Although the results of these two studies coincide with the accepted public health notion that smoking is unhealthy, there is no consensus in the scientific community on whether smoking has an independent causal role in the etiology of cervical cancer.
This example brings up an important concern: to what extent has Steen accurately represented the current status of scientific thinking on the other 200 topics included in his book? The public has no way of knowing.
The ranking process used in the book is also troublesome. Steen uses the size of the P value as his measure of validity, thus ignoring the more likely challenge; namely, confounding. Steen also groups cancers by incidence, and uses the group number (1 through 5) as a multiplier applied to the relative risk from the study with the smallest P value to provide the ranking number. But prostate and bladder cancers are grouped together (group #4) despite the fact that the incidence of prostate cancer (132,000 cases) is much closer to that of colon cancer in group #5 (156,000 cases) than it is to bladder cancer (51,600 cases) in group #4, which, itself, is much closer to uterine cancer (45,500 cases) in group #3. The result is a ranking of risks that is nearly as arbitrary as the group cut-off points themselves.
A Frustrating List
Perhaps most frustrating, however, is the fact that Steen's final list of risk factors for preventable cancers (page 269) and his list of "what to do" to prevent those cancers do not match up. He describes several strategies (pages 273 and 274), from stopping smoking to learning the 10 warning signs of cancer, but ignores at least 9 items listed earlier as preventable risks. These include: exposure to DDT, stress, use of oral contraceptives, eating more carbohydrates, eating fewer calories, having children, and exposure to black hair dyes. All were identified by Steen's method of selecting evidence and his ranking scheme.
It is unclear why these items were not transferred from the list of risks to the list of preventive strategies. Perhaps some do not offer preventive promise. If so, then it is reasonable to question the way in which they were identified. On the other hand, perhaps Steen simply overlooked them or made some other unspecified judgment regarding their validity or reasonableness. In either case, this book provides the public--for whom it was written--with one more reason to be confused about what should be done to prevent cancer.